Hu Jiandong

Laser sintering of green compacts

Abstract Green Compact Laser Sintering (GCLS) is a new technique for sintering powder metallurgical components by laser irradiation. After mixing; powders are pressed into a green compact; which can then be sintered by laser irradiation. The properties of powder metallurgical alloys for GCLS and conventional sintering are compared.

Laser sintering of Cu-Sn-C system P/M alloys

The Cu-Sn-C system P/M alloys were sintered by laser. The influence of laser sintering on the properties of the laser-sintered materials was investigated. The properties, such as the density, impact toughness, hardness and wear resistance of the laser-sintered materials are desirable. A maximum impact toughness of 11.7 J/cm2 was achieved and the wear resistance of the laser-sintered materials was tremendously increased compared with conventional sintering. The green compact made from Cu-Sn-C powders, with a thickness of 10 mm, can be penetratively sintered by using a suitable processing condition. The laser sintering was characterised by a thermal cycle which was accomplished in a relatively short time, resulting in a relatively high temperature (950 °C). The curves showing temperature profiles for the top surface and bottom of the laser-sintered specimen were recorded by thermocouples. Differences in temperatures between the top surface and bottom were very small, less than 60 °C. Some intermetallics/phases such as α-Cu, Cu31Sn8(δ), Cu4Sn(ε) and Cu6Sn5(η) were most readily produced in the laser-sintered materials and their distributions were more homogeneous than conventional sintering, owing to the better flow ability of the melt caused by a relatively high sintering temperature. The behaviour of diffusion between Cu and Sn was also studied by means of simulation diffusion couple.

Pearlite-like eutectic of ZL 108 aluminium-silicon alloy containing rare-earth elements rapidly solidified by laser

A lot of work on the eutectic structure in cast aluminium alloys has been carried out. However, no pearlite-like eutectic structure has been reported so far. This kind of structure was found when observing the laser-melted zone of the material by TEM. The material used in the present study was aluminium silicon eutectic alloy ZL 108. Its chemical composition in wt% is 12Si, 1.00Fe, 1.23Cu, 0.5Mn, 0.93Mg and 0.1 rare earth (RE). The RE contains 10wt% Ce

Twin structure in laser-melted Al-Si alloy containing rare earths

Aluminium and its alloys have been known as kinds of materials with high stacking-fault energy. It is therefore difficult to find stacking faults or twins in them. It was shown by our early studies that apart from a pearlite-like A1-Si eutectoid structure [1], a large amount of stacking faults [2] was found in laser-melted A1-Si alloy containing rare earths (RE). Following these results, we performed experiments with both the same material as in [1, 2] and laser-melted material coated with alloy powder containing RE. A twin structure was observed by transmission electron microscopy (TEM). The purpose of this letter is to display the twin morphology and to discuss possible mechanisms for twin formation. The materials used for laser melting were divided into two groups. The composition of the first group (FG) was (wt %): 12 Si, 1.23 Cu, 0.5 Mn, 0.93 Mg, 1.0 Fe and 0.1 RE. The RE contained 10 wt% Ce, the remainder being A1. The second group (SG) were prepared from laser alloying. Alloy powder was predeposited on the surface of the material, which was similar to the first material but without RE. The powder contained (wt %): 55 A1, 25 Si, 10 Cr and 10 RE (Ce-rich). Laser melting or alloying was carried out with an HG1-CO2 laser. The output power was 2.8 kW and the beam diameter 5 mm with a scanning speed of 54 mms -1 . Slices for TEM were cut from laser-melted alloyed zones with a thickness of 0.4 mm parallel to the melted surface. After thinning by a series of SiC papers, the thin foils were then thinned by ion-miiling or electrolyte (5% perchloric acid and 75% ethanol). A model H-800 TEM was employed to study microstructure, operated at 200 kV. The laser melted/alloyed region was 0.8 mm deep and 4.0ram wide, and the secondary dendritic distance of the melted region ranged from approximately 2 to 3.5 ram. Growth of the eutectic and 0~-A1 was based on the interface between liquid and solid (matrix). The growth direction of ol-A1 was in agreement with [0 0 1] orientation. Fig. 1 shows the o~-A1 and AI-Si eutectic for the laser-melted region (FG). The typical twin morphology in o~-A1 is shown in Fig. 2a and b, using brightand dark-field techniques. The electron diffraction pattern and its

Structural stability and stacking faults in a laser-melted ZL108 Al-Si alloy containing rare earth

The ZL108 Al-Si alloy containing rare earth was melted with a CO2 2 kW laser. The maximum microhardness values of the laser-melted zone (LMZ) was shifted back by 2 h in the microhardness-time curve and 20 °C in the microhardness-temperature curve, as compared with conventional treatment materials in the given range. The LMZ had better structural stability at the elevated temperature than that of the conventional materials. Stacking faults were found in the resolidified aluminium, and were identified to be intrinsic. Both structural stability and the existence of the stacking faults were related to Ce supersaturation in the resolidified aluminium.